While surplus lines direct premium written in 2016 generated growth of 2.8% in 2016, the report notes surplus lines premium rose to $42.4 billion — the highest point in history.

"Once again, the surplus lines segment has hit a new record level of U.S. premium," said Brian Van Cleave, president of the Derek Hughes/NAPSLO Educational Foundation. "The report continues to highlight our segment's financial resilience and strong financial performance in relation to the broader property and casualty industry, including thirteen years of no financial impairments."

The top 25 groups writing U.S. surplus lines are full of familiar names such as Nationwide and Berkshire Hathaway. Notable mergers in 2016 shifted groups higher on Best's rankings. One example was the merger of XL Group and Catlin, propelling the combined entity into the top 10.